1. Field of the Invention
This invention relates to printing presses and, in particular, this invention relates to clutch systems for UV modules used in printing presses.
2. Background of the Invention
Ultraviolet-sensitive ink is used widely in the printing industry. One reason for its use is that ultraviolet-sensitive ink can be quickly cured by being irradiated with ultraviolet light. Such irradiation is accomplished by directing a light beam, containing high proportions of ultraviolet light, at the printed substrate.
Lamps used to generate light for this purpose also generate considerable amounts of other energy in the form of heat. This heat is usually of little consequence when a printing press is operating, because the light and heat are directed toward the substrate which is in motion during the printing process. However, if the heat and light generated by the lamp is directed at a nonmoving substrate for a sufficient amount of time, the substrate is damaged, often to the point of the ignition. Additionally, other nonmoving components of the printing press may be damaged by the high amount of heat generated from the lamps. When the printing press operation must be halted, for example to clear obstructions or replenish ink supplies, the light generated by the lamp must be prevented from impinging the substrate. One way to prevent irradiating nonmoving substrate is to power down the lamp. However, considerable time is necessary for the lamp to generate sufficient irradiation to cure the ultraviolet-sensitive ink when power is restored. Consequently, preventing irradiation from impinging nonmoving substrate when a printing press is halted has been accomplished by housing the lamp in a structure having shutters, which can be opened to allow irradiation or closed to prevent irradiation from leaving the structure.
As stated above, intense heat is generated by the UV lamp during operation. These high-energy lamps require high-voltage and fairly high current, some requiring 3000 volts and 17 amps and may generate temperatures of 1000 degrees Fahrenheit during operation. Consequently, the structures housing these high-energy lamps are subjected to periods of the extremely high temperatures. These high temperatures inescapably cause the metal components of these structures to expand and warp. One consequence of this expansion and warpage is failure of these structures to properly operate.
UV module shutter assemblies of the prior art were usually a “rigid” rotary mount design, which did not allow for expansion or warpage of the pair of aluminum shutter extrusions. Since these shutters expand, band, and warp various magnitudes, the prior art rigid mounting arrangement caused the shutter drive train gear assembly to be forced out of alignment. This misalignment resulted in premature gear wear, coolant leakage, and shutter drive train binding. A bound shutter drive often left the shutters substantially locked into a position other than that desired. Moreover, any amount of coolant leakage, no matter how small, led to a myriad of problems such as electrical shorting and fires. Development of a shutter end cap with the specific seal and bearing arrangement working in conjunction with the instant clutch and rounded drive pin significantly reduced these leakages, wear, and binding problems.
Additionally, drive trains for UV module shutters of the prior art often require extensive adjustment during manufacture and maintenance so that breakpoint torques will be at desired levels. This extensive adjustment is time consuming and often results in improperly adjusted clutches due to the complexity of design.
Accordingly, there is then a need for a shutter clutch which will not bind and which does not require extensive adjustment during manufacture and maintenance.